1. Field of the Invention
The present invention relates to a method for the production of a fiber reinforced plastic structure, and more particularly to a method for defoaming resin-impregnated fibers and to a steering wheel which is used in the likes of an automobile, which is obtained by this method.
2. Description of the Background
The expression "fiber reinforced plastic structure" defines a product which is obtained by initially impregnating a continuous long-staple fiber such as a roving or strand with liquid resin, and then winding the impregnated fiber around the periphery of a reel or jig until the resultant bundle reaches a fixed thickness. The wrapped bundle is then allowed to harden, and then the hardened bundle is removed from the reel or jig as described in GB No. 2,004,835, for example. Since this structure enjoys freedom of design and is suitable for fabrication in many different configurations of one through three dimensions, efforts have been continuing toward the development of applications of the structure in various fields.
An objective in automobile manufacture is to achieve reductions in weight, and this can be achieved by reducing the weight of the various parts from which automobiles are manufactured. In this regard efforts are being made to prepare insert members for steering wheels which are light weight and which have high strength by using continuous long-stable fibers of the likes of high tension glass fibers, carbon fibers, or aromatic polyamide fibers represented by Kevlar in combination with a synthetic resin such as an unsaturated polyester resin, epoxy resin, or phenol resin.
During the course of the manufacture of such a fiber reinforced plastic structure as described supra, however, when a resin impregnated fiber bundle is formed by repetitively winding rovings around a winding jig composed of a central shaft 1, a fixing device 2, an arm 3, and a hook 4 as illustrated in FIG. 4, for example, the force, which compresses the bundle of rovings in the axial direction of the linear empty portion of the fiber bundle, namely in the direction perpendicular to the tensile strength of the roving as indicated by the arrow in the diagram, is not sufficient. Thus, air is entrapped within the resin impregnated fiber bundle 5. The air so entrapped is prevented from being expelled by the viscous layer of liquid resin. Even after the bundle has been hardened, the air remains within in the form of bubbles. The bubbles impair the strength of the fiber reinforced plastic structure and, therefore, prevent the product structure from acquiring sufficient strength.
A method is known by which entrapped bubbles remaining within the bundle encrusted with the resin can be reduced in number. The method involves feeding out the roving, impregnating the roving with resin, and winding the roving under vacuum. Thereafter, the bundle produced is allowed to stand under normal atmospheric pressure or increased atmospheric pressure in order to achieve a notably effective defoaming of the structure as a whole. However, the technique requires a large apparatus. This method, however, is not satisfactory when ample defoaming of specific portions of a given structure is desired. Further, the fiber reinforced plastic structure obtained by this conventional method generally has the drawback that it possesses a random cross section and, therefore, fails to withstand external forces which are brought to bear on the linear portion thereof.
The insert member of the above mentioned steering wheel is prepared using the winding jig 10 constructed as illustrated in FIG. 5. The number is prepared from a continuous long-staple fiber bundle impregnated with resin which is wound a stated number of times around jigs 14 and 15 to form a ring part and a metallic hub 9 along the route indicated by the arrows in the diagram as illustrated in FIG. 11. When the fiber bundle is wound in a fashion so that it passes alternately around the metallic hub 9 as illustrated in FIG. 5, the base of each of the spoke parts 12 of the insert member 11 is parted so that the cross section taken along the direction II-II in the diagram assumes the shape of a two-prong fork as illustrated in FIG. 12. When the insert member of this nature is covered with a resin sheath to form a steering wheel, the steering wheel which is produced does not have sufficient strength and rigidity. A need therefore continues to exist for an improved technique of preparing fiber reinforced plastic structures.